A research program is proposed which examines several aspects of the transport, distribution and metabolism of vitamin D and its metabolities. This proposal seeks to acquire specific and detailed information about the delivery and metabolism of antiricket sterols, and to apply these findings, where possible, to the study of human physiology and disease. Two major areas of research are proposed. Project one aims to examine, by means of new or existing specific assays for vitamin D metabolites, the physiologic and pathologic influences which control vitamin D metabolism in man. Serial examination of vitamin D metabolite concentrations in human serum is designed to further our diagnostic and therapeutic capabilities in clinical disorders of mineral homeostasis. Project two deals with the serum and tissue binding proteins for antiricketic sterols, and aims to examine the specific nature of sterol transfer into tissues. Studies are designed to isolate binding proteins, examine the regulation of their synthesis, explore the possibility of specific interactions between serum binding proteins and cell surface and intracellular proteins, and examine the interaction of sterol-binding complexes with intra-cellular organelles.